The present invention relates to an apparatus and method for treating a surface of a workpiece using plasma discharge wherein the apparatus is movable about the workpiece during treatment and operable at atmospheric pressure.
Plasmas, such as are described herein, are partially ionized gases and consist of ions, electrons and neutral species. Plasma is state of matter produced by the action of DC or AC fields having RF or MW frequencies. Plasmas can be useful for treating the surface of a workpiece.
Low power density, low intensity plasmas, such as dark discharges and corona discharges, have been used at low pressure and at one atmosphere for the surface treatment of various materials. However, due to the relatively low energy density, these discharges alter surface properties of materials relatively slowly, if at all. Also, corona discharges are non-uniform and filamentary in nature. This may lead to localized arcs known as xe2x80x9chot spotsxe2x80x9d and non-uniform surface modification. Generally, the use of corona discharges for treating the surface of a workpiece is unsatisfactory.
Glow discharge plasmas are produced by free electrons energized by an imposed DC, photon beam or RF electric field. This field causes electrons to collide with the neutral species. These collisions form a variety of active species which may include, excited atoms and molecules, metastables, free radicals, molecular fragments, electrons and ions, as well as ultraviolet and visible photons.
Glow discharge plasma has been successfully used in low pressure environments (e.g., below 10 Torr). In many applications, glow discharge provides active species which produce important effects, but generates temperatures high enough or requires treatment times long enough to damage the surface of the workpiece being treated.
Glow discharge plasmas are typically generated in low pressure environments. This constraint usually necessitates the treatment of workpieces within a vacuum system. Alternatively, glow discharge plasmas may be generated, for example, using the one atmosphere uniform glow discharge plasma reactors described in U.S. Pat. Nos. 5,387,842 and 5,403,453, both issued to Roth, et al, on Feb. 7, 1995, and Apr. 4, 1995, respectively.
Most of this work has been performed in a laboratory environment and has been limited to very small scale operations. The workpiece is limited to the size of the chamber. To treat a workpiece of any size, such as a garment, the chamber must be large enough to allow the garment to be disposed within the chamber. Generally, this will require the vacuum system to be big, bulky and expensive. Furthermore, such a chamber is typically stationary and thus requires the workpiece to be moved and placed within the chamber. This type of system cannot be used with a stationary workpiece.
Plasma treatments, such as plasma etching, deposition, cleaning or sanitization of a workpiece, can change the surface properties of the workpiece. Plasma etching can remove small amounts of material from the surface, thereby also removing surface contaminants and/or exposing a fresh surface for subsequent processing. Plasma etching can be used for applications such as sterilizing, cleaning, etc. of surfaces of a workpiece. Plasma-cleaned surfaces may provide for adhesion of electroplated layers or paint and stronger adhesive bonding of substances to the surface. Plasma etching may be useful for skin cleaning, hair cleaning, window cleaning, etc. Plasma etched surfaces may have modified moisture uptake properties, useful in applications such as household painting, nail polishes, hair coloring, skin moisturizing, etc.
Plasma deposition can deposit a thin layer or coating on the surface of a workpiece, providing improved surface properties such as hydrophobicity, hydrophilicity, oleophobicity or oleophilicity. Such surface properties may provide stain resistant fabrics, or superabsorbent material on the substrate. Plasma deposited coatings can be used on a variety of workpieces such as shoes, carpets, upholstery, decks, etc.
U.S. Pat. No. 5,961,772 iss. Oct. 5, 1999 to Selwyn and U.S. Pat. No. 6,262,523 B1 iss. Jul. 17, 2001 to Selwyn et al., disclose an atmospheric-pressure plasma jets using cylindrical and planar electrodes, respectively. DE 19,605,226, discloses a device to generate plasma using a plurality of parallel electrodes protruding from a surface. U.S. Pat. No. 5,236,512, issued Aug. 17, 1993 to Rogers, et al. discloses a device for cleaning a surface by introducing a highly reactive gas mixture to the surface. These teach devices having a single electrode pair/gas flow channel which makes it difficult to effectively treat a large surface area.
WO 01/44790 published Jun. 21, 2001 in the names of Korfiatis et al teaches a plasma reactor having at least one segmented electrode. In the reactor, a fluid passes through caplillaries and impinges on the surface of a dielectric. After impinging on the dielectric, the fluid changes direction and exits from the reactor. This arrangement provides the disadvantages that plugging of the capilaaries may occur and significant deposition on the wall of the dielectric may occur, and cause undesirable deactiviation of any active species in the fluid. U.S. Pat. No. 6,005,349 issued Dec. 21, 1999 to Kunhardt et al. teaches a glow pasma apparatus having a perforated dielectric with micro-channel apertures therethrough and separating two electrodes.
U.S. Pat. No. 5,671,045 issued to Woskov et al. on Sep. 23, 1997, and U.S. Pat. No. 6,081,329 issued to Cohn et al. on Jun. 27, 2000, disclose atmospheric pressure microwave plasma devices. These devices are used to activate atoms for trace element monitoring and analysis of solid, liquid and gas samples, based on the principles of the atomic emission spectroscopy. The device does not include a plasma enhancer or process chamber for treating a surface of a work-piece. Furthermore, these references fail to teach deposition/polymerization/etching, or other surface modifications.
The present invention provides an atmospheric-pressure, plasma generating apparatus and method to treat a surface of a workpiece. The present invention also provides an atmospheric-pressure, plasma generating apparatus and method to treat a surface of a workpiece, wherein the apparatus is movable about the surface of the workpiece during treatment.
In one embodiment the invention copmrises an atmospheric-pressure, plasma generating apparatus for treating a surface of a workpiece. The apparatus comprises:at least one powerable electrode connectable to a power supply and powerable by the power supply , at least one groundable electrode connectable to a ground and a dielectric intermediate the powerable electrode and groundable electrode. A first plurality of powerable electrodes and groundable electrodes 50 are disposed in pairs, each pair generating a plasma zone and operatively associated with a second plurality of flow channels, whereby a plasma gas can flow through the flow channels and thereby produce a plasma therein upon interaction with the powerable electrode when it is powered. The plasma is capable of interacting with a working gas to produce an excited species. A third plurality of outlets from the flow channels, allow the excited species to exit the flow channels. The outlets are juxtaposable with a workpiece whereby the excited species may flow through the outlets to impinge on the surface of the workpiece. The flow of the excited species occurs in a primary direction which is straight and unobstructed from the plasma to the surface of the workpiece. In another embodiment the invention comprises a method of treating a surface of a workpice in accordance with the foregoing.